On FindMyPast (which has free access this weekend) there are two 1938 records for the name Arthur James Derry. No record images, though.
Service number - 1430083
Service number - 1515904
Royal Regiment Of Artillery
In case you haven't seen it yet, there's an AJD (born 1913) in the 1921 census.
Looks to be in a foster care situation.
Thank you, from what we have been told we believe he and his sister were sent to a scattered home from the work house, I have not seen the 1921 census as I don't have full access to it at present, as far as we know he was a motorbike messenger with the royal signals during the war but like many of the veteran's he didn't talk about his time there.